Prostaglandins having a carbon atom replaced by nitrogen are disclosed in U.S. Pat. No. 3,973,566, U.S. Pat. No. 3,975,399 and in Tetrahedron Letters No. 43, 3853, 1976. In these cases however the substitutions occur at the cyclopentane ring moiety (position 8 and 12), while the side chains are unmodified. The derivatives disclosed in the prior art are to be considered as pirrole and pirazole derivatives, while the invention compounds still pertain to cyclopentane series.